Toward Sustainability Of Agrolandscapes

There exists the need to integrate and interface natural, agricultural, urban, and suburban systems if humans are to manage agrolandscapes in a truly sustainable manner. How might we approach this problem? Agricultural practices should increasingly be devoted to the preservation of natural areas (e.g., forests) and to the planting of a diversity of food and grain crops near the outer perimeter of our large cities (i.e., should view agricultural planning in conjunction with, rather than against, the planning of perimeter highways and other modes of transportation). Traditionally, urban and rural landscapes were interrelated in a mutual, sustainable infrastructure. Urban areas were frequently directly linked to the watershed or drainage basin because of transportation needs (rivers or lakes) or geological nodes (mineral deposits) of significance. Urban "sprawl" into the agricultural landscape tended to decouple this connectivity and sustainability. Rather than serving as an ecological/economic barrier, the suburban patch should provide a critical link to restore habitat patch connectivity (Fahrig and Merriam, 1985) and to promote societal sustainability (Barrett, 1989).

Urban areas contain human and natural resources that once again must become integrated with the agrolandscape to the extent that the city can be sustained by both economic capital (gross national product, employment, property values) and natural capital (primary productivity, biotic diversity, solar energy, and sludge usage as natural fertilizers). We refer to this perspective as "dual capitalism." Economic and ecological capital must become integrated; otherwise the resulting oxbow urban areas will increasingly become drained of aesthetic and natural resources. Ecosystem processes will increasingly become disconnected and/or diminished from the vital flow of energy, information, or biotic diversity that once connected the landscape system as an integrated whole.

The integrity of the architecture, the efficiency of the natural processes, and the quality of materials typically found within city boundaries (Kaplan and Kaplan, 1982) also have been reduced or degraded during this fragmentation process. Ecol-ogists frequently note "that the ecosystem is greater than the sum of its parts." Perhaps the landscape level of organization is now no longer greater than the sum of its parts. Isolated urban patches exhibit greater entropy (poverty and crime) and require greater subsidies (financial and human) to maintain their existence (Jake and Wilson, 1992). Isolation and fragmentation impede the attainment of ecological literacy (Orr, 1992) necessary to understand how natural regulatory mechanisms enhance the reestablishment of diversity (ethnic, biological, and ecological) which, in turn, is necessary to maintain agrolandscape functional processes. It has become increasingly critical to understand these relationships and regulatory mechanisms more fully. To do so, greater emphasis should be placed on suburban patches in an effort to integrate and reconnect urban and agricultural processes. Suburban "eco-tones" provide the opportunity to help transform the total landscape unit. Suburban areas are not marginal or isolated places, but increasingly central locations in the contemporary world (Baumgartner, 1988). Table 1 contrasts urban, agricultural, natural, and suburban systems and suggests that suburban areas be designed and managed based on our understanding of how natural ecosystems are structured and how they function.

Figure 4 depicts how this suburban area might be designed to interface with a transportation network, including the establishment of an enriched food crop, forestry, and recreational diversity that function as an economic/ecological transition area between the urban and rural landscapes. Landscape corridors, both natural (streams and trails) and human built (highways and mass transportation), will further enhance these linkages (Little, 1990).

Landscape corridors (linkages) manifest various configurations depending on natural phenomena, cultural preferences, or historical development (Hough, 1990). Corridors may connect a sequence of congruent patches. For example, corridors of an ecological mosaic have been defined as disturbance corridors (e.g., power lines), planted corridors (e.g., shelterbelts), regenerated corridors (e.g., fence-row succes-sional vegetation), remnant corridors (e.g., strips of native or climax vegetation) and resource corridors (e.g., riparian areas) (see Barrett and Bohlen, 1991, for details regarding corridor types). These corridors also may reflect or parallel land-use

Table 1 Contrasts among a Traditional Heterotrophic Urban System, an Autotrophic Conventional Agricultural System, a Natural Mature Ecological System, and a Well-Planned Integrated Suburban System

Attribute

Urban

Agricultural

Natural

Suburban

Primary

P/R< 1

P/R> 1

P/R= 1

P/R> 1

productivity

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